Field of the Invention
The present invention relates generally to a cutting apparatus, and more particularly to a cutting apparatus for hollow fibers embedded in and extending through a potting material fluid tightly in a manufacturing process of a hollow-fiber permeability apparatus such as a hemodialyzer for an artificial kidney.
To selectively separate materials through a membrane on the basis of their different permeabilities, there have been proposed an effective method in which polymeric hollow-fiber membranes showing a selective permeability are used. This method is useful, for example, as a hemodialyzer which serves to help a patient suffering from renal failure out of his death, because the use of the hollow fibers brings in a large effective surface area for the small size of the apparatus. In such apparatus, numerous hollow fibers made of cellulose membrane or acrylonitrile copolymer are closely bundled and disposed into a housing having a cylindrical or a rectangular cross section. Both end portions of the hollow-fiber bundle are respectively fixed to both end portions of the housing in fluid-tight relationship with a solidifiable liquid (potting material) having a suitable elasticity in a solidified state. The potting material consists of a polymer composition of epoxy resin, polyurethane, silicone resin and so on. The hollow fibers are disposed substantially parallel with each other and longitudinally along the length of the housing with their end portions extending through the solidified potting material. After the solidifiable liquid is solidified or heat-treated, each hollow fiber embedded in the potting material is cut perpendicularly to the longitudinal direction of the fiber so that the end of the fiber may be opened in a cut-surface thereof. In an operation of manufactured hemodialyzer, the blood of the patient is passed through the interiors or hollow portions of the hollow fibers from the openings at the cut-surface, while a dialysate is passed along the exteriors of the hollow fibers, whereby various metabolic wastes in the blood are dialyzed through the hollow-fiber membranes.
One of the most difficult problems in the assembling process of the above-described permeability apparatus is the cutting of the potting portion. The difficulty is particularly due to the nature of the potting material. The inventors have found that when the cutting is done in a conventional way using, for example, a ham cutter, the end portions of the hollow fiber are considerably rubbed with a cutting edge at the cut-surface and at the openings formed therein. The cutting also causes clogging of the openings of the hollow fibers, separation of the hollow fibers from the potting material at the boundary therebetween, or uneveness of the cut-surface. The reasons for these phenomena are considered as follows. The potting material or resulting scraps thereof are partially melted and softened due to heat evolution by the mechanical cutting so as to cover and clog at least a part of the openings of the hollow fibers during the rotation of the cutting blade. And, the separation of the hollow fibers from the potting material at the boundary there-between and the uneveness of the cut-surface are caused due to shearing stress developing by the friction between the surface of the blade and the cut-surface of the potting portion.
These defects result in several serious troubles when the selective permeability apparatus is applied to hemodialysis. The blood is essentially liable to clot when contacting with foreign substances and this blood clotting is accelerated under disturbance of the blood flow. In general, when the renal failure patient is subjected to a dialysis therapy, the blood clotting often appears. It has been observed that the clotting develops and grows from uneven portions at the cut-surface of the hollow fibers, even if heparin is used as an anti-clotting agent. Such uneven portions involve, as described above, that the cut-surface is not smooth, the hollow fibers are slightly separated from the potting material by cutting, the cutting position of the hollow fiber (cut-surface of the hollow fibers) is dislocated from the surface of the potting material. The grown clotts of the blood cover the openings of the hollow fibers, and a part of the clotts separated intrudes into the hollow portions of the hollow fibers. In this case, the blood can not flow through the hollow portions to reduce dialysis efficiency and finally, the dialysis operation becomes impossible.
Since having intrinsic tackiness and elasticity as seen in rubber, the potting material such as polyurethane, silicone rubber or epoxy resin clings or sticks to the cutting blade on the cutting operation, and smooth cutting can not be effected. This is a phenomenon which appears also in cutting a block of, for example, polyurethane, and further which causes a trouble in cutting the polyurethane together with the hollow-fiber bundle of cellulose embedded therein and extending through as in the hemodialyzer.
Since the cellulose hollow fiber has a considerably high rigidity whereas the polyurethane has tackiness and elasticity, these materials have quite a different behavior against the cutting blade. This will be now explained with reference to FIG. 1 to FIG. 3. As shown in FIG. 1, when hollow fibers 2 buried in a potting material 1 are cut with a cutting blade 3 in the perpendicular direction to the longitudinal direction of the fiber, a part of the elastic potting material 1 is first cut and the hollow fiber 2 then starts being cut. However, as shown in FIG. 2, the hollow fiber 2 is liable to bend at the contacting portion with the cutting blade 3, without being cut. This is due to the larger rigidity of the hollow fiber 2 than that of the potting material 1 having elasticity. For this reason, the hollow fiber 2 is partially separated from the potting material 1 at the cut-surface thereof so that a cleft 4 is formed between the hollow fiber 2 and the potting material 1. The cleft is not formed at the opposite side of the hollow fiber 2 because the hollow fiber 2 is pressed to the potting material 1. However, as the hollow fiber 2 is cut in the bent state as aforesaid, the cut-surface obtained is not satisfactory smooth as shown in FIG. 3 wherein the cleft 4 remains and a slant cut-surface of the hollow fiber 2 extends therefrom. Accordingly, a cut-surface 5 is not flat at the opening of the hollow fiber 2 and the end of the hollow fiber 2 is projected from other flat parts of the cut-surface 5.
The blood clotting can not be avoided in the conventional hemodialyzer with the potted portion having the cross-section pattern shown in FIG. 3. In addition, the cutting operation shown in FIGS. 1 and 2 has some defects that the operation is not suitable for mass treatments and that the wear of the cutting blade is unavoidably increased.